Electric filter



w m c. E. G. BAHLEY 2,481,562

' ELECTRIC FILTER I Filed 5, 1945 2 Sheets-Sheet 1 AT T ORNEY C. E. G. BAILEY ELECTRIC FILTER Sept. 13,, 1949.

'2 Sheets-Sheet 2 Filed Aug. 23, 1945 (FLUSJQQYEB HMOZVD 65131 1151 BAILEY mvmss 4 FILTER OUTPUT INPUT INVENTOR.

ATTORNEY Patented Sept. 13, 1949 UNITED STATES gATENT ()FFICE ELil'iitIc Fiixifift Christopher Edmund- Gervase Bailey, Bournemouth; Hants, England, assig-uor to The Hartford National Bank & Trust Company, Hartford, Conn, as trustee Application Afigust 23, 1945-; Serial No: 612,273

In Great Britain September 4; 1941 v swam 1-; P'iibli Law 690} August s; 1946 Patent ares Septtriber 42 19:61 9 claim. (01. ivi sfi) rvefsm of aItema-tehalf waves of the mint cut:

rent of the desired mean fr eque'tieir,

Sh-duld itbe u'ndes"irabl for the apiiara'tus cbiiibiii-fig the row-ease fii'te'f'tb be notified at the frequency 6f the: Shaft, slip; fing s" may be mounted 6n the sfiaft and brushes biougiit t6 b'ar' on these sup rings t6 make mafia] c'bri nection' to the mw-pass" filter. I v V In some cases undesirable" electricaf difs tufliiances may arise from unavoidable irregiiia'tities iii the (idfitafi between" er iifiiut to 1 6i slip tinge anti trustee. Tlis may a l'ded bi) replaiing the direct ednneetion fr 'bhisiies t6 cdnamnta tdts or sligi rings by afimutate d1 capacitive 00111511112.

In order that the ini entioh may be rfieie feed enamew time nee flaming in that fig re.

. Fig. 2, the Raw-pee filter] is s tationary anclis connected to the commutators 2, 3 by slip ring l, 8; ill when are daft led on the same shaft i the cmmutato'rs 2, 3 and are directly eon fietc'i'tb the plfl tli'f'e'df. Th Slip rings 1, 8*, M ake eii'iaed by s tatidnawylii'ushes H, [2, l3, It which are dii'ctl'y bnneetd to the lbw-pause filter I.

The ifect' in' bbththe altioxre-tiserib'edaffane merits is the same and is sli'o'wri gmpmeauy in F18. 4.

.Ai-lieintit' half WEVQ'S (if a Sii'lllSbidjl E. MP: F. having the mean freauemy ate i'vrsed in Sign by the'ebinnii t-atoif 2 as irsiesemed" in Fig; 4(a); and this reversed is" anfiliedto'the'inbiit o'f theiow-pa s's fi-lter t. The oiit iit oi the low-1525s filter 4 will; if the" pa e liafitiis? lot? en'ouh' iii frequency, consist of an almost constant E. M. F. as represented in Fig. 4(2)). This will in turn be periodically reversed by the commutator 3 giving a square-topped wave form as represented in rig. etc).

Any M. F. of slightly difierent frequency will be periodically reversed in a non-synchronous manner. its average value, appearing at the output or the low-pass filter, W111 therefore slowly vary and, by making the attenuation of the filter high at the irequency or this variation, the output can be made ektreinely small. Thus the resultant squai e-top iurm or varying amplitude can be also made extremely small.

The enectiveness of the electro-mechanical filter described above is only governed by the useful attenuation at very low frequencies of the lowpass filter, and the inevitable losses in the lowpass riiter itself ah'ect only the power efficiency of the whole device, and not its effectiveness as a filter. Hence, for some purposes it will be sufficient to make this filter of a series resistance arm followed by a shunt capacitance arm.

It will be apparent that the filter as described is responsive also to all odd harmonics of its mean frequency; and that the square-topped wave form likewise contains all the odd harmonics of this frequency. In cases where this property is objectionable an electro-mechanical filter as described may be preceded and followed by additional lowpass filters having a cut-ofi frequency between the mean frequency and its third harmonic. The difficulties hereabove described as inherent to the construction of purely electrical filters of narrow discrimination do not arise in these additional low-pass filters, which are only required to discriminate between frequencies whose ratio is 3:1.

With arrangements as described with reference to Figs. 2 and 3, undesirable electrical disturbances may in some cases arise from unavoidable irregularities in the contacts between commutators and brushes or between slip rings and brushes. There disturbances may be avoided by replacing the direct connection from brushes to commutators or slip rings by an inductive or ca- 4 pacitive coupling of the character illustrated in Figs. 5 to 8.

Fig. 5 shows an inductive coupling to replace a commutator. The shaft l carries a two-pole armature is having a winding [6 and surrounded by a stator I? having a two-pole field winding 18 of a conventional type.

Fig. 6 shows an inductive coupling to replace a slip ring. The shaft l carries an armature IS on which a helical coil is wound co-axially with the shaft. This coil is surrounded by a stationary coil 2! which is also helically wound coaxially with the shaft and is carried by an armature 22. The armatures are preferably ferromagnetic.

Fig. 7 shows a capacitive coupling to replace a commutator. The shaft I carries a pair of semicircular vanes 23, 24, which are perpendicular to the shaft. These vanes 23, 24 cooperate with parallel semi-circular fixed vanes 25, 26.

Fig. 8 shows a capacitive coupling to replace a slip ring. The shaft I carries an annular vane 2! perpendicular to the shaft and co-operating with a parallel fixed annular vane 28.

' The external connections and method of operation with inductive or capacitive couplings are similar to those described with commutators and slip rings with reference to Figs. 2 and 3.

As shown in Fig. 9, when employing inductive means in an arrangement equivalent to Fig. 2,

a pair of inductive devices of the type illustrated in Fig. 5 is provided, which devices serve the same function as that performed by the commutators in Fig. 2. The rotor windings [6 of the two devices are intercoupled through low-pass filter 4, the input being fed to the stator windin i8 of one device and the output being taken from the stator winding l8 of the other device. In Fig. 10, there is shown an inductive arrangement analogous to that in Fig. 3, a pair of couplers of the type shown in Fig. 6 being provided to serve the same function as the slip rings in Fig. 3. The low-pass filter 4 is connected between the stator coils 2| of the couplers, the rotor coil 20 of one coupler being connected to the rotor winding [6 of the input device, and the rotor coil 20 of the other coupler being connected to the rotor winding l6 of the output device.

As shown in Fig. 11, when employing capacitative means in an arrangement equivalent to that in Fig. 2, a pair of capacitative devices of the type illustrated in Fig. 7 is provided, which devices serve the same purpose as the commute.- tors in Fig. 2. The rotor vanes 23 and 24 of the two devices are intercoupled through low-pass filter 4, the input being impressed on the stator vanes 25 and 23 of one device and the output being derived from the stator vanes 25 and 2B of the other device. In Fig. 12 there is shown a capacitative arrangement analogous to that of Fig. 3, two pairs of capacitative couplers of the type shown in Fig. 8 being provided to serve the same function as the slip rings in Fig. 3. The low-pass filter i is connected between the stator discs 28 of one pair of couplers and the stator discs 28 of the other pair of couplers. The rotor discs 2? of the one pair of couplers are connected respectively to the rotor vanes 23 and 24 of the input device, while the rotor discs of the Other pair of couplers are connected respectivel t the rotor vanes 23 and 24 of the output device.

From the description with reference to Fig. 4 it will be apparent that in putting the present invention into practice, the reversal of the input current should occur not only at the same periodicity as the selected frequency but also in phase with the component of that frequency in the composite input current, so as to obtain the desired reversal of alternate half-waves as represented in Fig. 4 (a).

Filters according to the present invention are specially applicable to direction finding apparatus of the kind described in co-pending patent application 570,656, now abandoned, the commutator shaft described above can be driven from rotating mechanism forming part of the said direction finding apparatus.

I claim:

1. Electrical apparatus for separating a current component of selected frequency from a composite current including a plurality of superimposed currents of different frequencies, comprising a polarity reversing member responsive to the selected frequency of said current for producing a cyclically varying current of constant polarity, a filter network coupled to said polarity reversing member for removing the cyclical variations in said cyclically varying current, and a second polarity reversing member coupled to said filter network for alternately reversing the polarity of the current derived from said filter network in synchronism with said first polarity reversing member.

- 2. Electrical apparatus-for separating a current component of a selected frequency from a 0 m? posite current including a plurality of superimposed currents of different frequencies, comprising a first commutator member for converting said composite current into a cyclically varying current of constant polarity, a filter network coupled to said commutator member for removing said cyclical variations in said cyclically varying current, and a second commutator member coupled to said filter network for alternately reversing the polarity of the current derived from said filter network in synchronism with said first commutator member.

3. Electrical apparatus for separating a current component of selected frequency from a composite current including a plurality of superimposed currents of different frequencies, comprising a shaft member driven at rate synchronous with said selected frequency, a first commutator member mounted on said shaft for converting said composite current into a cyclically varying current of constant polarity, a filter network coupled to said commutator member for removin said cyclical variations in said cyclically varying current, and a second commutator member coupled to said filter network for alternately reversing the polarity of the current derived from said filter network in synchronism with said first commutator member.

4. Electrical apparatus for separating current component of selected frequency from a composite current including a plurality of currents of different frequencies, comprising a shaft member driven at a rate synchronous with said selected frequency, a first commutator member having two segments mounted on said shaft for converting said composite current into a cyclically varying current of constant polarity, a filter network coupled to said commutator member and mounted on said shaft for removing said cyclical variations in said cyclically varying current, and a second commutator member having two segments mounted on said shaft and coupled to said filter network for alternately reversing the polarity of the current derived from said filter network in synchronism with said first commutator member.

5. Electrical apparatus for separating a current component of selected frequency from a composite current including a plurality of superimposed currents of different frequencies, comprising a shaft member driven at a rate synchronous with said selected frequency, a first commutator member having two segments mounted on said shaft for converting said composite current into a cyclically varying current of constant polarity, a filter network mounted independently of said shaft and coupled to said commutator member for removing the cyclical variations in said cyclically varying current, means for coupling said filter network to said commutator member, a second commutator member having to segments and mounted on said shaft, and means for coupling said filter network to said second commutator member whereby said second commutator member alternately reverses the polarity of the current derived from said filter network.

6. Electrical apparatus for separating a current component of a selected frequency from a composite current including a plurality of superimposed currents of different frequencies, comprising a shaft member driven at a rate synchronous with said selected frequency, a first two pole electromagnetic structure mounted on said shaft for converting said composite current into a cyclically varying current of constant polarity, a filter network coupled to said electromagnetic structure for removing the cyclical variations in said cyclically varying current, and a second two-pole electromagnetic structure mounted on said shaft and coupled to said filter network for alternately reversing the polarity of the current derived through said filter network in synchronism with said first electromagnetic structure.

7. Electrical apparatus for separating a current component of selected frequency from a composite current including a plurality of superimposed currents of different frequencies, comprising a shaft member driven at a rate synchronous with said selected frequency, an inductively coupled polarity reversing member mounted on said shaft for converting said composite current into a cyclically varying current of constant polarity, a filter network mounted independently of said shaft and coupled to said polarity reversing member for removing the cyclical variations in said cyclically varying current, inductive coupling means for connecting said filter network to said polarity reversing member, a second inductively coupled polarity reversing member mounted on said shaft, and a second inductive coupling means for coupling said second polarity reversing member to said filter network whereby said second polarity reversing member alternately reverses the polarity of said current derived through said filter network in synchronism with said first polarity reversing member.

8. Electrical apparatus for separating a current component of selected mean frequency from a composite current including a plurality of superimposed currents, comprising a shaft member driven at a rate synchronous with said selected frequency, a capacitatively coupled polarity reversing member mounted on said shaft for converting said composite current into a cyclically varying current of constant polarity, a filter network coupled to said polarity reversing member for removing the cyclical variations in said cyclically varying current, and a second capacitatively coupled polarity reversing member coupled to said filter network for alternately reversing the polarity of the current derived through said filter network in synchronism with said first polarity reversing member.

9. Electrical apparatus for separating a current component of selected frequency from a composite current including a plurality of superimposed currents comprising a shaft member driven at a rate synchronous with said selected frequency, a capacitatively coupled polarity reversing member mounted on said shaft for converting said composite current into a cyclically varying current of constant polarity, a filter network mounted independently of said shaft and coupled to said polarity reversing member for removing the cyclical variations in said cyclically varying current, a capacitative coupling means for connecting said filter network to said polarity reversing member, a second capacitatively coupled polarity reversing member mounted on said shaft, and capacitative coupling means for connecting said second polarity reversing member to said filter network whereby said second polarity reversing member alternately reverses the polarity of said current derived through said filter network in synchronism with said first polarity reversing member.

CHRISTOPHER EDMUND GERVASE BAILEY.

No references cited. 

